Allow passing in author to add-exercise script (#146)

bin/add-exercise

@@ -2,9 +2,9 @@
 
 set -euo pipefail
 
-if (( $# != 1 )); then
+if (( $# < 1 )); then
     echo >&2 "Populates a new directory for a practice exercise."
-    echo >&2 "Usage: $0 <exercise-slug>"
+    echo >&2 "Usage: $0 <exercise-slug> [author]"
     exit 1
 fi
 
@@ -39,8 +39,13 @@ end-of-tests
 ;with
 END_TEST
 
-echo 
-read -rp 'Your github username: ' author
+if (( $# < 2 )); then
+    echo
+    read -rp 'Your github username: ' author
+else
+    author="${2}"
+fi
+
 conf="exercises/practice/${slug}/.meta/config.json"
 jq  --arg author "${author}" \
     '.authors = [$author]' "${conf}" > "${conf}.tmp" \